I liked:
* The setting. I have no direct experience with boarding schools but I like to imagine that they are just like Bullworth (or, Rushmore) with tasteful student uniforms, brick buildings, on-campus dorms, and oak banisters.
* The unique identities for other students. Even though many students are pretty generic in how they behave, it still increased the sense of immersion that each student on campus had a different character model.
* The changing seasons. Again, it increased the sense of immersion and also allowed for cool Halloween and Christmas missions.
* The satire. Rockstar usually does a good job of making authority figures look ridiculous, which I enjoy. Sure, there's some heavy handed dialogue but there is also subtler stuff in there.
* The art teacher (boners!), and art class (qix!).
* The clothes you could get looked pretty cool, although Rockstar included a 'boxer short' skin that they seem to think is hilarious and is actually just dumb.
* The way your room filled up with trophies from different missions.

I did not like:
* The GTA style mission system where the main character gets treated like a bitch. I realize that they are trying to tell a particular story and must corral the player through a certain sequence of events, but I wish they write it so that the player feels like they are doing things for their own reasons and not just getting bossed around by every douche in town.
* The location of the bike garage. When I would head into town I never seemed to have my bike close by, so I'd end up skateboarding or stealing the first bike I saw. I would have preferred it if they had your bike stashed right at the main gate.
* Shop class. Sometimes I'd fail even though I was certain that I was hitting all the buttons, Brainiac. I think the 'rotate L3' animation is misleading because it looks like a lazy swirl but you actually need to spin it pretty fast in order for the move to register.
* The greaser clique. When I was in school I knew jocks, nerds, rich kids, and tough kids but I never knew 50's style car enthusiasts. I don't think the game is specific about what decade it's set in, but they seemed out of place. Possible better clique ideas - theater kids, marching band, goth kids.

When discussing a game it's always easier to identify the negative things than the positive things, but really I enjoyed the game quite a lot. If you spend 30 hours playing a game and when you are done your criticism is "bike garage too far from main gate", then that indicates that there is quite a lot of stuff to enjoy.